1. Field of the Invention
This invention relates to rubber compositions having excellent rubber toughness, tire sidewall reinforcement and/or adhesion to tire cords employing high imino and/or methylol functional self-condensing alkylated triazine resin additives in the substantial absence of resorcinol or resorcinol equivalent coreactants.
2. Related Prior Art
A widely used organic rubber additive for improving adhesion of vulcanized rubber to brass coated steel cords and polyaramide or polyester cord comprises the combination of hexamethoxymethylmelamine and resorcinol. In addition, hexamethylenetetramine is sometimes used in combination with resorcinol. Those combinations of organic compounds are quite effective for the purpose, but the use of resorcinol presents malodorous and possibly toxic hazards during rubber processing due to excessive fuming of resorcinol.
Resorcinol-free vulcanizable rubber compositions are known. For example, U.S. Pat. No. 5,298,539 discloses vulcanizable rubber compositions containing uncured rubber, a vulcanizing agent and at least one additive selected from the group consisting of derivatives of melamine, acetoguanamine, benzoguanamine, cyclohexylguanamine and glycoluril monomer and oligomers of these monomers. These derivatives are substituted on average at two or more positions on the monomer or each unit of the oligomer with vinyl terminated radicals and the composition is free of resorcinol.
Another manner of eliminating resorcinol from vulcanizable rubber compositions has relied on the use of alternative coreactants. U.S. Pat. No. 4,038,220 describes a vulcanizable rubber composition which comprises a rubber, a filler material, N-(substituted oxymethyl)melamine and at least one of .alpha. or .beta. naphthol. This reference employs the monohydric phenols, .alpha. or .beta. naphthol, as methylene acceptors in the resin forming reaction during vulcanization in the absence of resorcinol. The use of resorcinol-formaldehyde resin to replace resorcinol in vulcanizable rubber compositions is also known. A. Peterson, et. al., "Resorcinol Bonding Systems For Steel Cord Adhesion", Rubber World (August 1984).
Despite the various proposals made to avoid the use of resorcinol in vulcanizable rubber compositions, there is a continuing need for vulcanizable rubber compositions containing commercially available cost effective additives that improve the adhesion of vulcanized rubber to tire cords and improve rubber toughness without the use of resorcinol.
None of the above-mentioned references disclose or suggest the use of high imino and/or methylol functional self-condensing alkylated triazine resins in vulcanizable rubber compositions in the absence of resorcinol as an adhesion promoter or rubber toughener.